Surface analysis for catalyst layer (PT/PTFE/C) and diffusion layer (PTFE/C) for proton exchange membrane fuel cells systems (PEMFCs)

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) studies have been used to analyze the surface of diffusion layer (PTFE/C) and catalyst layer (Pt/C/PTFE) of electrode. Detail analysis of carbon C_1s peak showed that the carbon was of the form of C, C-O, CO, CF, CF₂ and CF₃ with CF₂ is more dominated on the surface compared to CF and CF₃. The oxygen O_1s photoelectron peak showed that the oxygen was of the form of CO and C-O. The platinum was of the form of Pt⁰ with some Pt oxidized to PtO. The scanning electron microscopy was used to observe the dispersion of Teflon in the diffusion layer, the distribution of platinum in the catalyst layer loaded with 0.38 mg Pt/cm² and also the cross section of the membrane electrode assembly. The prepared electrode delivers a superior performance compared with the commercial electrode (E-TEK). The difference in performance between the two electrodes is due to the good localization of the platinum particles.     

Constrained stabilization: an enlargement technique of positively invariant sets

This paper presents a new technique of enlargement of positivelyinvariant sets for linear systems with input saturation. Thistechnique is based on the use of the convex hull of the unionof N preconstructed positively invariant sets. It is shown thatthe obtained region is a stability region where the controlis always admissible.     

Reactions of 2-Pyrones with 7-Aminoindazole: The First Synthesis of N-(1H-7-Indazolyl)-pyridinones

New N-(1H-7-indazolyl)-pyridinones have been prepared by the condensation of 2-pyrone derivatives with 7-aminoindazole in the presence of acid medium. They have been characterized by means of ¹H and ¹³C NMR, IR, and mass spectroscopy. The structure of the compounds and the mechanism of their formation are reported.     

Equivariant functions and integrals of elliptic functions

In this paper, we introduce the theory of equivariant functions by studying their analytic, geometric and algebraic properties. We also determine the necessary and sufficient conditions under which an equivariant form arises from modular forms. This study was motivated by observing examples of functions for which the Schwarzian derivative is a modular form on a discrete group. We also investigate the Fourier expansions of normalized equivariant functions, and a strong emphasis is made on the connections to elliptic functions and their integrals.     

A new analytical formula to compute the step length of Padé approximants in the ANM: Application to buckling structures

In this paper, we propose a new analytical formula to define the next branch in the Asymptotic Numerical Method (ANM) using the Padé approximants. The proposed formula is based on the computation of the relative error of two consecutive Padé approximants. This formula is obtained by developing the relative error with respect to the path parameter. An appropriate matrix formulation is adopted for the computation of this relative error. A comparison between the analytical formula proposed in this paper and the classical continuation Padé approximants using the step length computed numerically using dichotomy method is presented for examples of buckling structures.     

Study of corrosion-erosion behaviour of stainless alloys in industrial phosphoric acid medium

The corrosion and corrosion-abrasion resistance of some stainless steels in industrial phosphoric acid 30% P₂O₅ has been studied using electrochemical techniques. The corrosion rate of materials increases with the increase of temperature. Alloys which contain chromium, molybdenum and nitrogen in sufficient quantities present the best behaviour.In the abrasion-corrosion conditions, the experimental device set up allowed to follow continually samples electrochemical behaviour. Under dynamic conditions and without solid particles, the increase of acid projection speed has no effect on the alloys corrosion behaviour. The adding of abrasive leads to a general increase of corrosion rate and to a decrease of material resistance. Under these conditions, materials attack is controlled by synergistic effect between the abrasion and the impurities. The cast 30% Cr shows good resistance according to his high chromium content.     

Hypersurfaces d'un fibré vectoriel Riemannien à courbure de Gauss prescriteHypersurfaces of a Riemannian vector bundle with prescribed Gaussian curvature

Let M be a compact Riemannian manifold, E a Riemannian vector bundle on M and Σ the sphere subbundle of E. We look for embeddings of Σ into E admitting prescribed Gaussian curvatures of various types. To cite this article: A. Hanani, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 927–930.     

Resistivity and thermoelectric power of molten aluminium: experiment and theory

The electrical resistivity?ρ?of metallic liquid aluminium is measured as a function of temperature. The measurement needs an experimental design able to get the resistivity of a very reactive liquid metal. Liquid aluminium seems to be a simple metal. We first interpret the experimental results by using an ab initio calculation of the electrical resistivity ρ(E) as function of the electron energy, taking into account recent exchange and correlation contributions in the framework of the generalized gradient approximation (GGA). But surprisingly the classical theoretical interpretation leads to an apparent inconsistency. Thus we discuss the sensitivity of the calculation on the inputs and propose improvements of the theoretical approach. They allow a better physical understanding of pure liquid aluminium which is absolutely necessary before undertaking the study of liquid aluminium alloys.     

Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.